Safes or vaults which employ concrete, heat insulating or filler materials in their wall structures are well known. Prior art patents representative of such security structures embodying filler materials include U.S. Pat. Nos. Re. 15,429; U.S. Pat. Nos. 1,400,104; 1,443,087; 2,134,861 and 2,492,422. A number of problems have been associated with concrete structures and methods of making them. For example, prior art concrete structures usually have a thick outer metal wall and a lighter inner wall between which a concrete mass has been poured and hardened. Concrete is a mixture of a binding paste and aggregate. The paste is mainly composed of cement and water. To make a concrete mass pourable or workable, there is an excess of water required. The water over and above that required to complete the chemical hydration or setting reaction is called "water of convenience" or "free water." This free water usually remains in varying amounts within the cement structure and presents a number of problems peculiar to the manufacture and use of security cement structures. First, such free water subjects the walls of a safe to liability of corrosion. Furthermore, it has been reported that free water sometimes causes sweating which is detrimental to the contents of the safe. Also, undesirable loss of concrete strength usually accompanies the presence of free water. In the cement curing process, furthermore, the free water will bleed within the concrete and emerge from the concrete surfaces. Bleeding water must be removed during manufacture and hinders efficiency. In addition, it is nearly impossible to determine the exact percentages of free water in the concrete mass without breaking down the structure of the safe; and as the free water remains in the concrete mass during a period of years, shrinkage usually takes place resulting in the cracking of the concrete mass. Therefore, avenues are open for the burglar to penetrate the weakened concrete mass. Shrinkage also occurs during the curing process of ordinary or standard concrete compositions and this causes the cement to shrink away from the internal walls or casing of the safe structure. Such shrinkage prevents a form-fitting composite and facilitates entry by various burglar means.
Additionally, a major disadvantage associated with known concrete safe liners or walls has been their unsatisfactory resistance to attack by acetylene torch or high temperature means. Upon exposure of known concrete masses to an acetylene torch, such masses tend to spall, disintegrate, or even explode. Spalling or disintegration of the concrete by torch renders the concrete very susceptible to subsequent penetration by chisel, hammer, drill or other tools. Even without torch penetration, known concrete structures are not satisfactorily burglar-proof. In short, improvements are needed.